1. Field of the Invention
The present invention relates to a capacitor in a semiconductor device and method of fabricating the same which prevents the resistance between its lower electrode and plug from increasing.
2. Discussion of Related Art
A variety of research has been performed for increasing the capacitance density of a semiconductor device to allow the capacitor to have a specific amount of capacitance even if the cell area becomes smaller as the device is more highly integrated. To obtain a large amount of capacitance, the capacitor""s lower electrode is formed in three-dimensional structure, for example, stacked or trench structure, enlarging the surface area of the dielectric of the capacitor. However, the stacked or trench structured capacitor is fabricated through a complicated process. Accordingly, there are limitations on increasing the surface area of the dielectric. To solve this problem, there has been developed a method of enlarging the capacitance in which the dielectric is made of a material of a high dielectric constant, such as Ta2O5, PZT(Pb(Zr Ti)O3), PLZT((Pb La)(Zr Ti)O3), PNZT(Pb(Nb Zr Ti)O3), PMN(Pb(Mg Nb)O3), BST((Ba Sr)TiO3).
FIG. 1 is a cross-sectional view of a capacitor according to a related art. Referring to FIG. 1, N-type impurity region 13 is formed in semiconductor substrate 11, which serves as source and drain regions of a transistor including a gate (not shown in the drawing). Insulating interlayer 15 is formed on semiconductor substrate 11 to cover the transistor. Contact hole 17 exposing impurity region 13 is patterned in insulating interlayer 15. Impurity doped polysilicon is filled in contact hole 17 to form a plug 19 which is electrically connected to impurity region 13. Specifically, plug 19 is formed in such a manner that the doped polysilicon is deposited through CVD (chemical vapor deposition) and then etched back using RIE (reactive ion etching), to expose interlevel insulating layer 15.
Barrier layer 21 and lower electrode 23 are sequentially deposited on insulating interlayer 15 including plug 19. Barrier layer 21 which comes into contact with plug 19 is formed of TiN or TaN. Lower electrode 23 is formed in a manner that an oxidation-resist metal like Pt, Mo or Au, or metal whose oxide has conductivity such as Ir or Ru is deposited on barrier layer 21. Barrier layer 21 prevents the metal forming lower electrode 23 from reacting with silicon composing plug 19 and forming silicide. This is because the silicide is easily oxidized to be changed into an insulating material.
Dielectric layer 25 is formed on insulating interlayer 15 to cover lower electrode 23. Dielectric layer 25 is formed of a material having a high dielectric constant, for example, Ta2O5, PZT(Pb(Zr Ti)O3), PLZT((Pb La)(Zr Ti)O3), PNZT(Pb(Nb Zr Ti)O3), PMN(Pb(Mg Nb)O3), or BST((Ba Sr)TiO3). Upper electrode 27 is formed of the same metal as lower electrode 23 on dielectric layer 25. When lower and upper electrodes 23 and 27 are formed of an oxidation-resist metal, they are prevented from being oxidized even if they come into contact with dielectric layer 25. When the electrodes are formed of the metal whose oxide has conductivity, their resistances do not increase because they have conductivity even when they are oxidized.
FIGS. 2A to 2D are cross-sectional views showing a method of fabricating the conventional capacitor. Referring to FIG. 2A, insulating interlayer 15 is formed on P-typed semiconductor substrate 11 including N-type impurity region 13 serving as source and drain regions of a transistor having a gate (not shown). The insulating interlayer 15 P-typed semiconductor substrate 11 copy is then patterned through photolithography, forming contact hole 17 exposing impurity region 13. Referring to FIG. 2B, impurity doped polysilicon is deposited by CVD on insulating interlayer 15, to fill up contact hole 17. In this case, the polysilicon comes into contact with the exposed impurity region 13 through contact hole 17. Thereafter, the polysilicon is etched back using RIE to expose insulating interlayer 15. By doing so, the polysilicon is left only in contact hole 17, forming plug 19.
Referring to FIG. 2C, TiN or TaN is deposited on insulating interlayer 15 to come into contact with plug 19, and form barrier layer 21. Oxidation-resistant metal like Pt, Mo or Au, or metal whose oxide has electric conductivity such as Ir or Ru is deposited on barrier layer 21, to form lower electrode 23. Here, barrier layer 21 prevents lower electrode 21 from being reacted with plug 19, thereby eliminating the formation of the suicide between barrier layer 21 and plug 19. Lower electrode 23 and barrier layer 21 are patterned through photolithography, to be left on a predetermined area of insulating interlayer 15 including contact hole 17. In this case, lower electrode 23 and barrier layer 21 are patterned to have barrier layer 21 come into contact with plug 19.
Referring to FIG. 2D, a material having a high dielectric constant, for example, Ta2O5, PZT(Pb(Zr Ti)O3), PLZT((Pb La)(Zr Ti)O3), PNZT(Pb(Nb Zr Ti)O3), PMN(Pb(Mg Nb)O3), or BST((Ba Sr)TiO3) is deposited on insulating interlayer 15 to cover lower electrode 23, thereby forming dielectric layer 25. Here, when lower electrode 23 is formed with oxidation-resistant metal, it is prevented from being oxidized even if it comes into contact with dielectric layer 25 having an oxygen component. When lower electrode 23 is formed with a material whose oxide has electric conductivity, such as Ir or Ru, its resistance does not increase because it has electric conductivity even when oxidized.
Oxidation-resistant metal like Pt, Mo or Au, or metal whose oxide has conductivity, for example, Ir or Ru, is deposited on dielectric layer 25, to form upper electrode 27. That is, upper electrode 27 is formed of the same material as lower electrode 23. When upper electrode 27 is formed with an oxidation-resistant metal, it is prevented from being oxidized even if it comes into contact with dielectric layer 25. When upper electrode 27 is formed with a material whose oxide has electric conductivity, its resistance does not increase because it has conductivity even when oxidized. Upper electrode 27 and dielectric layer 25 are patterned, being left only on a portion corresponding to lower electrode 23. Only the portion of dielectric layer 25, which is placed between lower and upper electrodes 23 and 27, is used as dielectric storing charges.
As described above, the capacitance of the capacitor according to the related art increases because the dielectric layer is made of a material having a high dielectric constant. However, oxygen for forming the material with a high dielectric constant is diffused through the sides of the barrier when the dielectric layer is formed, to oxidize the barrier layer. This increases the contact resistance between the plug and lower electrode.
Accordingly, the present invention is directed to a capacitor of a semiconductor device and method of fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a capacitor which prevents the contact resistance between the plug and lower electrode from increasing due to oxidation of the barrier layer.
Another object of the present invention is to provide a method of fabricating a capacitor, which prevents the barrier layer from being oxidized, to keep the contact resistance between the plug and lower electrode from increasing.
To accomplish the objects of the present invention, there is provided a capacitor of a semiconductor device, which includes a semiconductor substrate, an insulating interlayer formed on the semiconductor substrate, the insulating interlayer having a contact hole which exposes a predetermined portion of the semiconductor substrate, a plug filled in the contact hole, the plug coming into contact with the semiconductor substrate, a contact layer formed on the insulating interlayer, the contact layer coming into contact with the plug, first and second barrier layers formed on the surface and sides of the contact layer, a lower electrode formed on the first barrier layer, a dielectric layer formed on the second barrier layer and lower electrode, and a upper electrode formed on the dielectric layer.
To accomplish the objects of the present invention, there is also provided a method of fabricating a capacitor of a semiconductor device, including the steps of forming an insulating interlayer on a semiconductor substrate and pattering it, to form a contact hole which exposes a predetermined portion of the semiconductor substrate, forming a plug in the contact hole, the plug coming into contact with the semiconductor substrate, sequentially forming a contact layer, first barrier layer and lower electrode on the insulating interlayer and pattering them to be left on the plug, the contact layer coming into contact with the plug, forming a second barrier layer on the sides of the patterned contact layer, and forming a dielectric layer and upper electrode on the lower electrode and second barrier layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.